Across the country, relatives, friends and members of the general public placed American flags and flowers on the tombs of soldiers who gave their lives for the country.

During his second Memorial Day as commander-in-chief, Trump placed a wreath at the Tomb of the Unknown Soldier.

He was joined by US Defense Secretary Jim Mattis and Chairman of the Joint Chiefs of Staff General Joseph Dunford for the ceremony at Arlington National Cemetery, whose rolling hills of greenery just outside the US capital are the final resting place for more than 400,000 veterans.

"Our fallen heroes have not only written our history -- they've shaped our destiny," Trump said. "They fought and bled and died so that America would forever remain safe and strong and free."

Los Angeles Mayor Eric Garcetti was among the speakers during an observance at his city's National Cemetery.

Besides Washington, some of the largest parades took place in Chicago and New York, with veterans' groups and bands among the participants. Chicago's celebrations have taken place since 1870.

In contrast to Veterans Day, which honors all who have served in the armed forces, Memorial Day pays tribute to fallen military staff.

On Sunday, tens of thousands of bikers in bandanas, cowboy hats or gleaming helmets descended on Washington to parade from the Pentagon past the military cemetery and ending at the Vietnam Veterans Memorial in honor of US soldiers missing in action in foreign wars, a now 30-year-old tradition by motorcyclists who dub themselves Rolling Thunder.

Among them are many Vietnam War veterans. Some of the bikers stopped by the National Cathedral for a "blessing of the bikes" service before they set about their humming business.

This year, there was also an effort to expand awareness of the Korean War and the Americans killed in that conflict.

A massive display of 645,000 poppies was placed behind glass on the National Mall -- the expansive grassy esplanade home to many of the city's monuments -- near the Korean War Memorial.

The display honors fallen military members and aims to raise awareness about the impact of war.

Memorial Day originated after the American Civil War that ended in 1865.